EFFECTS OF INBREEDIXG A:N'D CEOSSBEEEDING. 5 



Lecord was made of the coat color patterns as a means of identification. This record 

 as later served as a means of noting certain family characteiistics, which, in many 

 ases, were transmitted to succeeding generations of inbred stock with quite uniform 

 jgularity. All animals of the foundation stock were between 5 and 6 months old 

 'hen mated. 



Twenty-fom- females of uniform size and conformation were selected and num- 

 ered consecutively from 1 to 24. The males were selected in a like manner and 

 imibered in another series beginning with 1. The number of each of these females 

 f the foundation stock was given to the family of guinea pigs which descended from 

 er. Generation 1 is the progeny of the foundation stock, and is, therefore, not 

 ibred. In order to follow the closest line of inbreeding, brother and sister of the 

 ime litter were mated. In all cases the best individuals in the litter were selected 

 »r breeders. Their progeny were selected and mated in a Like manner. This method 

 being continued, and at present (1913) indi\T.duals in a few of the families have 

 aen inbred for 13 generations. All breeders in each of the families have been inbred 

 u-ough 4 generations. 



In Family 4, parents were bred to their progeny; that is, sires were mated with 

 leir daughters, granddaughters, etc., of each succeeding generation dmingthe breed- 

 ■g period of their lives. In a similar manner dams were mated with their sons, 

 andsons, etc., of succeeding generations. 



In Test 2 of this experiment the animals of the foundation stock were unrelated to 



£h other. Some of the breeders were selected from the same general stock at the 



/ireau of Animal Industry Experiment Station as were those in Test 1, but in all 



, ses they were mated with stock which was obtained from a different soiu-ce. The 



!,ien stock was apparently as healthy and vigorous as the other. The foundation 



nales used in this test were nmnbered consecutively from 31 to 42, inclusive. The 



nilies were numbered in the same manner as those in Test 1. All animals were 



used, fed, and cared for in the same manner. Practically no change has been made 



the method of rearing our breeding stock since the experiment was started. The 



jthods which we use are those which have been followed successfully for the past 



years by the Bureau of Animal Industry Exj^eriment Station, where thousands of 



i inea pigs are raised annually for laboratory piu-poses. 



[t was found that more satisfactory results could be obtained by having one male 

 i i only one female occupy each breeding cage, because frequently two females gave 

 1 th to young at about the same time, making it impossible to tell to which female 

 t ; young belonged. In all such cases these mixed litters were eliminated from the 

 « oeiiment. In afew instances young females became pregnant by their sires before 

 1 sy were weaned, which was at the age of 33 days. Young from these matings were 

 £ eliminated from the experiment. 



According to this report, 35 families were started, 24 wholly from 

 t3 line-bred stock of the Bureau of Animal Industry and 11 from a 

 pss between this stock and guinea pigs obtained from a local 

 caler. All were carefully selected, for vigor, from large stocks. 

 1 all but one family, matings were made exclusively between full 

 t others and sisters. The data from Family 4, in which matings 

 Vi re made between parent and offspring, have not yet been analyzed. 

 Si^en of the remaining 23 famihes in Test 1 (from the line-bred 

 Si ck) went out of existence before the second generation was pro- 

 d^ed, for various reasons, such as the early death of the female or 

 t', failure to produce living young of both sexes. Four of the 12 

 fi lilies in Test 2 failed for similar reasons, and another was disposed 



